Anaplasmosis is a tick-borne bacterial infection in dogs caused by two species of Anaplasma bacteria, each targeting different blood cells and producing different symptoms. It’s one of the more common tick-borne diseases veterinarians test for, and most dogs recover well with antibiotic treatment. Here’s what you need to know about how dogs get it, what it looks like, and what to expect.
Two Types of Canine Anaplasmosis
There are actually two distinct forms of this disease, caused by two different bacteria. The more commonly diagnosed form is caused by Anaplasma phagocytophilum, which infects a type of white blood cell called neutrophils. This form is known as canine granulocytic anaplasmosis and tends to cause the classic symptoms most people associate with the disease: fever, lethargy, joint pain, and loss of appetite.
The second form is caused by Anaplasma platys, which specifically targets platelets, the tiny blood cells responsible for clotting. This form causes a condition called infectious canine cyclic thrombocytopenia, where platelet counts drop in repeating waves roughly every one to two weeks. The first wave is typically the most severe, with anywhere from 31% to 63% of platelets becoming infected. After that initial spike, the cycles tend to become milder as the dog’s immune system mounts a response, though the pattern can continue for weeks.
How Dogs Get Infected
Dogs contract anaplasmosis through tick bites. A tick needs to remain attached for 24 to 48 hours before it can transmit the bacteria, which is why prompt tick removal is one of the most effective ways to prevent infection. After transmission, it takes one to two weeks for symptoms to appear.
Both deer ticks (also called black-legged ticks) and brown dog ticks are primary carriers. Geography matters: anaplasmosis is most common in regions with high tick populations, particularly the northeastern United States, the upper Midwest, and parts of the Pacific coast. But cases occur wherever these ticks live, including across Europe.
One important thing to know: you cannot catch anaplasmosis directly from your dog. The bacteria spread through tick bites, not through contact with an infected animal. That said, if your dog tests positive, it means infected ticks are active in your environment, and those same ticks can bite you. Anaplasmosis does affect humans, and it’s spread by the same tick species.
Common Symptoms
The most frequently reported signs of anaplasmosis in dogs are:
- Fever
- Lethargy
- Decreased appetite
- Dehydration
- Lameness or joint pain
Lameness is particularly associated with the granulocytic form (A. phagocytophilum) and can shift from one leg to another, sometimes resembling Lyme disease. Vomiting and diarrhea also occur in some dogs. In rare cases, more serious signs develop, including nosebleeds, neck pain, or seizures.
Dogs with the platelet form (A. platys) may show very few outward symptoms between thrombocytopenic episodes. Some dogs develop spontaneous bruising or small hemorrhages on the gums or belly when platelet counts bottom out, but many infected dogs appear relatively normal between cycles. This makes it easy to miss without blood work.
Not every infected dog gets sick. Some dogs are exposed and develop antibodies without ever showing clinical signs. These subclinical carriers can test positive on routine screening and create a confusing situation for owners who have a perfectly healthy-looking dog with a positive test result. Your vet will typically look at blood work and symptoms together before deciding whether treatment is needed.
How It’s Diagnosed
Most veterinary clinics use a combination blood test (often called a SNAP test) that screens for anaplasmosis antibodies alongside other tick-borne diseases like Lyme and heartworm. These in-clinic tests have a sensitivity above 93% and specificity above 98%, making them a reliable first step.
A positive antibody test means your dog has been exposed to the bacteria at some point, but it doesn’t necessarily confirm an active infection. Antibodies can persist for months or even years after exposure. If your dog is symptomatic, the vet will usually combine the SNAP test with a complete blood count looking for low platelet counts, low white blood cell counts, or other abnormalities.
For confirming active infection, PCR testing is more sensitive than trying to spot the bacteria directly under a microscope. PCR detects the organism’s genetic material in a blood sample and can distinguish between active infection and past exposure. This test is typically sent to an outside laboratory and takes a few days for results.
Treatment and Recovery
Doxycycline is the standard antibiotic for anaplasmosis in dogs. Treatment courses typically run 14 to 28 days depending on the severity of infection and whether there’s concern about co-infection with other tick-borne organisms like the one that causes Lyme disease. Dogs commonly pick up more than one tick-borne infection at the same time, since the same tick can carry multiple pathogens.
Most dogs start to improve within 24 to 48 hours of starting antibiotics. Fever drops, energy returns, and appetite picks up quickly. This rapid response is actually so characteristic that it’s sometimes used as a diagnostic clue: if a dog with suspected anaplasmosis doesn’t improve on doxycycline within a couple of days, the vet may reconsider the diagnosis.
Full recovery is typical for dogs treated promptly. Platelet counts and white blood cell counts generally return to normal within days to weeks. Some dogs continue to test positive on antibody tests long after the infection has cleared, which can be confusing at future vet visits but doesn’t necessarily mean the dog is still sick.
Co-Infections With Other Tick-Borne Diseases
Because the ticks that carry Anaplasma also transmit other pathogens, co-infection is a real concern. Lyme disease is the most common overlap, since both are carried by the same black-legged tick. Dogs with both infections may have more severe symptoms or take longer to recover. This is one reason vets often run a panel that tests for multiple tick-borne diseases simultaneously rather than checking for just one.
If your dog tests positive for anaplasmosis, it’s worth confirming that testing for Lyme, ehrlichiosis, and heartworm was included. The treatment approach may change if more than one infection is present, though doxycycline happens to be effective against several of these organisms.
Prevention
Tick prevention is the single most effective way to protect your dog. Year-round tick preventatives, whether oral, topical, or collar-based, dramatically reduce the risk of transmission. Since the bacteria require 24 to 48 hours of tick attachment to transfer, products that kill or repel ticks quickly offer the best protection.
After walks in wooded or grassy areas, check your dog thoroughly. Ticks favor spots around the ears, between toes, under the collar, and in the groin area. Remove any ticks you find immediately with fine-tipped tweezers, pulling straight out without twisting. The faster a tick comes off, the lower the chance of disease transmission.
Annual screening through your vet’s routine blood work is also worthwhile, especially if you live in a tick-heavy region. Catching exposure early, even in a dog that seems fine, gives you and your vet the chance to monitor blood values and intervene before symptoms develop.